It has been an unrealized aim of synthetic polymer chemists to prepare multiphase block copolymers with well-defined hard and soft segment structures, block molecular weights, molecular weight distributions and architectures. Such copolymers would preferentially display phase separated microphase morphologies with a sharp interface between hard and soft phases. Investigation of the structure-morphology-property relations in these types of well-defined block and segmented copolymers has been one of the most active areas of research for over 40 years. Such polymer chemistry today is an important field both for academic and industrial interests and most probably will continue to be in the next decades.
Synthesis, characterization and structure-morphology-property relations in segmented polydimethylsiloxane-urea (also termed as PDMS-urea or silicone-urea) and silicone-urethane copolymers have been investigated for over two decades. Due to the substantial differences between the solubility parameters of polydimethylsiloxane [15.6 (J/cm3)1/2 or 7.6 (cal/cm3)1/2] and urea [45.6 (J/cm3)1/2 or 22.3 (cal/cm3)1/2] segments, it has been possible to design model silicone-urea copolymers with very good phase separation and a sharp interface between PDMS and urea phases. As well documented in the literature, in order to get the desired microphase morphologies important factors that need to be controlled include block molecular weights and their distribution and the hard/soft segment ratio in the copolymer. For silicone-urea copolymers there has seemed to be a critical PDMS molecular weight of about 2,500-3,000 g/mole in order to achieve good phase separation.
Certain methods for preparation of segmented copolymers, and certain segmented copolymers, have been known, such as certain segmented copolymers, which consist of a hard (e.g. urea or urethane) and a single soft segment (e.g. polyether, aliphatic polyester or PDMS). In some cases, in addition to the main soft segment (e.g. a polyether), system may be modified with small amounts of a second soft segment (e.g. PDMS). See, e.g., E. Yilgor and I. Yilgor, Polymer, 42(19), 7953-7959 (2001); E. Yilgör, E. Burgaz, E. Yurtsever and I. Yilgör, Polymer, 41(3), 849-857 (2000); U.S. Pat. No. 5,792,554 (Aug. 11, 1998).
However, in such segmented copolymers, incorporation of the second soft segment thus far has been random and construction of the resulting copolymer otherwise has been less controlled than would be desirable.